Specialized transporting epithelia, e.g., intestine and kidney, mediate the movement of nutrients, ions, water and excretory products in multicellular organisms and thus, play an important role in the maintenance of overall homeostasis. Recent evidence indicates that toxic environmental pollutants, such as, organochlorines and heavy metals, accumulate in sensitive bird and fish epithelial tissues and that osmoregulatory, nutrient and excretory transport is inhibited. Unfortunately, the primary functional sites of pollutant action remain largely unidentified because of the limited information that is obtained from transport inhibition experiments with intact tissues. Recent developments in the field of membrane biology now make it possible to separate functionally and morphologically distinct regions of epithelial cell membranes and to study transport in vesicles formed from these membranes. Since these procedures permit the investigator to manipulate driving forces, e.g., electrical and chemical gradients, in the absence of cellular metabolism, inhibitor effects on individual transport processes can be quantitated. The objective of this project is to identify DDT and heavy metal sensitive sites in bird and fish epithelia using these powerful new procedures to complement standard physiological and biochemical techniques, such as, transport studies in intact tissues and ATPase determinations. The proposed research will be focussed primarily on three questions related to pollutant toxicity in lower vertebrate: 1) Is DDT (and possibly heavy metal) inhibition of salt, water and neutral amino acid transport in marine teleost intestine a result of action at a brush border carrier or a basal-lateral Na,K-ATPase; 2) Do DDT and heavy metals inhibit the transport of organic acids in teleost kidney by acting at a membrane carrier or the Na,K-ATPase; 3) Does DDT thin eggshells in membranes. Answers to these questions are expected to provide important insights into the fundamental mechanisms by which toxic pollutants act.